Multi-sensor relief valve well test system

ABSTRACT

A well testing system is described which comprises a ball valve (10) having a plurality of fluid lines coupled thereto (20a, 20b, 20c). The ball valve (10) is located between a process fluid flow line (16) and a vent line (18) with each fluid line (20a, 20b, 20c) being coupled to a respective piece of well-test equipment rated at a certain pressure value. Pressure relief means (22a, 22b, 22c) are located in each fluid line (20a, 20b, 20c) between the piece of equipment and said ball valve (10) and each pressure relief means (22a, 22b, 22c) is operable when the in-line fluid pressure exceeds a predetermined value to pass said fluid to said ball valve (10). The ball valve (10) is actuatable in response to any one of said pressure relief means (22a, 22b, 22c) having fluid passed therethrough whereby the ball valve is actuated to an open position and remains in the open position once actuated, so that the well reservoir fluid/gas mixture from said fluid flow line (16) passes through the ball valve (10) to said vent line (18).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to process safety equipment forhydrocarbon production and in particular, but not exclusively, to amethod and apparatus for use with existing well test equipment ontemporary process installations.

2. Description of the Related Art

In conventional well testing a considerable amount of equipment istransported to an oil rig and a well test/process situation is set up totest the fluid from the downhole reservoir. A typical prior art testsystem is shown in FIG. 1 where a number of well test components such asa steam exchanger, a test separator and a surge tank are provided aspart of the well test equipment. As each component has a differentpressure rating--it is important to monitor the pressure in each of thecomponents such that if an over-pressure situation occurs at any pieceof equipment, a safety valve is actuated which vents the over-pressurefluid to atmosphere via the rig relief burner boom. With the systemshown in FIG. 1 separate safety valves are coupled to each component. Ifthere are a large number of components this will require an equallylarge number of safety valves and the monitoring and coupling of suchvalves is a disadvantage in a rig environment. In addition, in existingwell test systems certain parts of the system are ignored and it isassumed that safety valves are not required to be coupled thereto, forexample the coil of the heat exchanger. In addition, the safety valvesare of the same design and are representative of the prior art.

A common safety valve used is the SPM emergency relief valve which is aspring-operated device using a hardened ball and seat sealing area. Theball is held fast against the seat by valve springs and remains seateduntil upstream pressure equals the set pressure. At this point the ballbegins to unseat to allow liquid to relieve. As upstream pressureincreases, the ball compresses a spring and travels away from the seatuntil an equilibrium is met that allows a given amount of liquid to passat a pressure above the valve setting. When the pressure drops below theset pressure, the valve reseats. These existing valves are primarilydesigned to vent liquid and they are not designed to vent multi-phasefluids, such as that in a hydrocarbon production line which is generallya fluid/gas mixture. In addition, these valves do not lock open and aredesigned for venting relatively low volume. When there is a liquid gasmixture combination and the fluid is at high pressure, thedepressurisation curve is very steep so that when the valve initiallyopens the throttling effect causes the temperature of the gas to fall tosuch a level that the fluid freezes up and venting does not occur. Inthis situation the pressure is retained and the well test equipment isthen likely to fail at the next weakest point which is probably thepiece of the equipment which the valve is intended to protect. Ingeneral the downstream side of each piece of equipment is not rated toan equal pressure as the upstream system and may rupture. In addition,these valves are not particularly accurate in pressure rating because atthe start the gas temperature may be -40° F. and this temperature canchange to +250° F. within half an hour to an hour of start up. Thevalves are not repeatable and the valve operating point changes becauseof thermal stress so that venting is or will be unpredictable.

A further problem with the prior art arrangement is that there is noin-line block valve which means that pressure tests can only be carriedout at a value less than the safety valve threshold with the result thatthe valve rating for a fully open position cannot be checked. With thearrangement shown in FIG. 1 only the part of the well test equipment towhich the valve is attached is protected and, consequently, many safetyvalves are required, for example in FIG. 1, six safety valves SV₁ -SV₆,are shown and this only provides partial protection for the system.

It is an object of the present invention to provide a well test systemin which the requirement of multi-safety valves is obviated and whichallows pressure testing to be carried out at and above the pressure tothe full value of the production line portion in which the valve issituated.

Another object of the present invention is to provide a relief valvewhich obviates or mitigates at least of the aforementioneddisadvantages.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, there is provided awell testing system comprising a ball valve having a plurality of fluidlines coupled thereto, said ball valve being located between a processfluid flow line and a vent line, each fluid line being coupled to arespective piece of equipment rated at a certain pressure value,pressure relief means located in each fluid line between the piece ofequipment and said ball valve, each pressure relief means being operablewhen the in-line fluid pressure exceeds a predetermined value to passsaid fluid to said ball valve, said ball valve being actuatable inresponse to any one of said pressure relief means having fluid passedtherethrough whereby the ball valve is actuated to an open position andremains in the open position once actuated, so that the well reservoirfluid/gas mixture from said fluid flow line passes through the ballvalve to said vent line.

Preferably, each fluid line is coupled to a separate piece of well-testequipment and said pressure relief means includes rupture disc meansrated for the pressure of the element to which it is connected.

Conveniently, each fluid line is provided by stainless steel tubingwhich may be stored in drums and rolled out for use. The stainless steeltubing line has conventional fittings on the end for connection to thewell test equipment.

Preferably, each ball valve includes an apertured ball element rotatablymounted in a valve housing, said ball element being rotatable inresponse to pressure from a line in which fluid passes through aruptured disc via a one way valve to rotate the ball element to an openposition and which remains thereat until reset.

Conveniently, the ball valve includes a cylindrical piston which isrectilinearly moveable, said piston being coupled to the ball element sothat in response to applied pressure from a fluid line, rectilinearmovement of the cylindrical piston is converted to rotary movement ofthe ball element.

Preferably, a plurality of fluid line inlet ports are disposed aroundthe periphery of valve housing, each of said inlet ports being adaptedto be connected to a respective fluid line, and said piston means beingresponsive to an increase in pressure from any of said ports to actuatesaid ball valve element to an open position.

Preferably also, a reset and/or observation port is disposed in saidvalve housing said reset port being adapted to be coupled to a furtherpressurised fluid line so that when pressure is applied, saidcylindrical piston and ball valve may be restored to a closed position.

According to another aspect of the present invention there is provided amethod of monitoring pressure a plurality of well test components in awell test arrangement and for relieving over-pressure from any monitoredcomponent, said method comprising the steps of:

providing a ball valve coupled between a flow line and a vent line,

coupling fluid lines between said ball valve and each piece of equipmentto be protected,

providing predetermined pressure relief means in each fluid line, thevalue of each predetermined pressure relief means being determined bythe rating of the piece of equipment to which it is coupled, and

actuating said ball valve to an open position in response to a signalfrom any pressure relief means so that flow from said flow line isvented through said ball valve to said vent line.

Preferably said method includes step of restoring said ball valve toclosed position after said over pressure has been vented through saidvalve.

According to another aspect of the present invention there is provided apressure relief valve for use in a well test system, said pressurerelief valve comprising a valve housing, an apertured rotatable ballelement which is captive in said valve housing, piston means located insaid valve housing, said piston means being coupled to the ball valveelement, at least one fluid line inlet port in said valve housing whichpasses through a wall of said housing, said at least one fluid lineinlet port being adapted to be coupled to a fluid line whereby saidpiston is moveable in response to pressure in said line exceeding apredetermined value, and movement of the piston within said valvehousing causes said ball valve element to rotate from an closed positionto an open position.

Preferably said pressure relief valves include a reset port located insaid valve housing, said reset port being adapted to be coupled toanother pressured fluid line for resetting the piston and moving theball to its closed position.

Preferably there are provided a plurality of fluid line inlet portsdisposed around the periphery of said valve housing, each of saidplurality of fluid line inlet ports being coupled to a fluid line sothat pressure in any one of said lines which exceeds the value for theequipment coupled to that line may actuate the cylindrical piston tooperate and open said ball valve.

Conveniently, said valve housing has a flange at each end to which thevalve housing can be coupled to a flow line and to a vent pipe.

BRIEF DESCRIPTION OF THE DRAWING

These and other aspects of the present invention will become apparentfrom the following description when taken in combination with theaccompanying drawings.

FIG. 1 is a schematic diagram of a well test system and safety equipmentin accordance with a prior art arrangement;

FIG. 2 is a schematic diagram of an embodiment of a well test system inaccordance with the present invention;

FIG. 3 is an enlarged and partly longitudinal sectional view of apressure relief valve shown in FIG. 2 in accordance with a preferredembodiment of the present invention; and

FIG. 4 is an enlarged side view of the ball valve taken in the directionof arrow A in FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference is first made to FIG. 2 of the accompanying drawings whichdepicts a preferred embodiment of a multi-sensor pressure relief valvein accordance with the present invention. The pressure relief valve,generally indicated by reference numeral 10, is coupled by flangeconnections 12 and 14 to a fluid flow line 16 and a vent pipe 18. As iswell known, the vent pipe 16 is fed out to the rig relief burner booms.The pressure relief valve 10 is a ball valve and has an apertured ballelement 11 disposed in a valve housing 21, has a plurality of fluidinlet lines connected thereto of which three, 20a, 20b and 20c, areshown. Each of the lines 20a, b, and c is connected to a particularpiece of equipment (not shown) which is desired to be protected fromover-pressure. Each line 20a, b and c is made of stainless steel whichmay be rolled from a drum during installation and is connected to piecesof equipment using existing tappings on the equipment. Each lineincludes a pressure sensor in the form of a rupture disc which isdisposed in rupture discs holders 22a, b and c. These discs are designedto rupture at a predetermined temperature and pressure and communicatethe over-pressure fluid to the safety relief valve 10.

If there is fluid over-pressure in any particular piece of equipment,then the disc in the fluid line connected to that piece of equipmentwill rupture and pressure is applied to the relief valve 10 to actuatethe ball valve element 19 therein to an open position so that pressurein flow line 16 is vented through the vent pipe 18 as will be laterdescribed in detail.

Reference is now made to FIG. 3 of the drawings which is a longitudinalsplit sectional view through the relief valve 10 shown in FIG. 1. Asmentioned above, the relief valve 10 is a ball valve which contains theapertured ball valve element 19 which is mounted by pivot pins 24 in thevalve housing, one of which is shown for rotation about the pin axis. InFIG. 3 the valve is shown in a closed position. The remaining valvestructure will best be described with reference to the operation of thevalve which occurs when there is an over-pressure situation.

The valve housing 21 is generally cylindrical and includes a pluralityof fluid inlet ports 26 disposed around the periphery of the housing,although only one is shown in the interest of clarity. The port 26passes through the wall of the housing 21 and each port isadapted/connected to a fluid inlet line (FIG. 2) which is also coupledto a piece of equipment in which the pressure is to be monitored.Disposed in the bore of the valve 10 is a moveable piston 28 and a valveseating arrangement generally indicated by reference numeral 30 which ismoveable up and down within the valve housing with piston 28. The piston28 has a threaded inside face 29 and is coupled to a cylindrical sleeve32 which is coupled to the seating arrangement 30 which, in turn, has aseating face 34 shown abutting the ball valve element 19.

In the event of over-pressure occurring in any particular line, forexample line 20b from the separator vessel such that the pressureexceeds 1400 p.s.i., the ruptured disc in holder 22b ruptures andpressure is applied to fluid inlet port 26. The pressure is applied tothe bottom face 36 of the piston 28, and because the other side of thepiston is at atmospheric pressure, the applied pressure forces thepiston 28 upwards within the bore of the valve 10. As the piston 28 isforced upwards it carries sleeve 32 and seating arrangement 30 upwardsuch that the valve seat 34 moves free of the ball element 19. Inaddition, as best seen in FIG. 4, as the valve seating arrangement 30moves upwards pins 38 which are located in oblique slots 40 in the ball19 and which cause the ball element 19 to rotate within the valvehousing 21 such that the central aperture 42 in the ball valve element19 clears the valve seat 34 so that fluid in the flow line 16 passesthrough the ball element aperture 42 and through the bore of the reliefvalve to the vent pipe 18.

As long as there is over-pressure the valve 10 remains fully open untilthe pressure in the system is reduced to zero. Once this occurs the ballvalve requires to be reset to the closed position and this is achievedby applying pressure to the observation and/or reset port 44, located inthe valve housing 21 above the fluid inlet port 36. When pressure isapplied to this port it acts on the upper surface 46 of the piston andforces the piston, sleeve 32 and seating arrangement 30 down so thatvalve seat 34 again seats against the ball element 11 which have beenrotated by the pin 38 and slot 40 arrangement to the closed position, sothat the valve is again ready for use.

Thus, it will be appreciated that a considerable advantage of thisarrangement is that a single pressure relief valve is used which islocated in the line which may be tested at and above the operatingpressure of the valve to the full value of the production line portionin which it is situated. In addition, various pieces of well testequipment may be coupled through fluid lines to the operating ports onthe safety valve element as required and each piece of equipment can beset to provide an over-pressure signal at a predetermined value byinserting a suitable value of rupture disc in the line. In addition,once the ball valve is actuated is remains in the fully open positionuntil reset and the relief valve can readily be inspected using theobservation port to see whether the valve is functional.

We claim:
 1. A well testing system comprising a ball valve having aplurality of fluid lines coupled thereto, said ball valve being locatedbetween a process fluid flow line and a vent line, each fluid line beingcoupled to a respective piece of equipment rated at a certain pressurevalue, pressure relief means located in each fluid line between thepiece of equipment and said ball valve, each pressure relief means beingoperable when an in-line fluid pressure exceeds a predetermined value topass said fluid to said ball valve, said ball valve being actuatable inresponse to any one of said pressure relief means having fluid passedtherethrough whereby the ball valve is actuated to an open position andremains in the open position once actuated, so that the well reservoirfluid/gas mixture from said fluid flow line passes through the ballvalve to said vent line.
 2. A system as claimed in claim 1 wherein eachfluid line is coupled to a separate piece of well-test equipment andsaid pressure relief means includes rupture disc means rated for thepressure of the element to which it is connected.
 3. A system as claimedin claim 1 wherein each fluid line is provided by stainless steel tubingwhich is stored in drums and rolled out for use.
 4. A system as claimedin claim 3 wherein the stainless steel tubing line has conventionalfittings on the end connection to the well test equipment.
 5. A systemas claimed in claim 1 wherein each ball valve includes an apertured ballelement rotatably mounted in a valve housing, said ball element beingrotatable in response to pressure from a line in which fluid passesthrough a ruptured disc via a one valve to rotate the ball element to anopen position and which remains thereat until reset.
 6. A system asclaimed in claim 5 wherein the ball valve includes a cylindrical pistonwhich is rectlinearly moveable, said piston being coupled to the ballelement so that in response to applied pressure from a fluid line,rectilinear movement of the cylindrical piston is converted to rotarymovement of the ball element.
 7. A system as claimed in claim 6 whereina plurality of fluid line inlet ports are disposed around the peripheryof valve housing, each of said inlet ports being adapted to be connectedto a respective fluid line, and said piston means being responsive to anincrease in pressure from any of said ports to actuate said ball valveelement to an open position.
 8. A system as claimed in claim 6 wherein areset and/or observation port is disposed in said valve housing saidreset port being adapted to be coupled to a further pressured fluid lineso that then pressure is applied, said cylindrical piston and ball valvemay be restored to a closed position.
 9. A method of monitoring pressurea plurality of well test components in a well test arrangement and forrelieving over-pressure from any monitored component, said methodcomprising the steps of:providing a ball valve coupled between a flowline and a vent line, coupling fluid lines between said ball valve andeach piece of equipment to be protected, providing predeterminedpressure relief means in each fluid line, the value of eachpredetermined pressure relief means being determined by the rating ofthe piece of equipment to which it is coupled, and actuating said ballvalve to an open position in response to a signal from any pressurerelief means so that flow from said flow line is vented through saidball valve to said vent line.
 10. A method as claimed in claim 9 whereinsaid method includes step of restoring said ball valve to closedposition after said over pressure has been vented through said valve.